Preparing levigated alumina for storing in water suspension



' as just described.

' Patented. 29," 1945' I UNITED STATES, PAT NT OFFICE PREPARINGLEVIGATED ALUMINA FOR s'roanvo IN WATER suspension Joseph R. Vilella,New York, N. I}, United States Steel Corporation or corporation oiDelaware No Drawing. Application March 25, 1942,

Serial No. 436,195

I 4 Claims. This invention is concerned with the problem I of storingleviaated alumina in a water solution so that it can be convenientlyused when desired 1 for extremely fine polishing purposes; particularly,for the polishing oi metallographic specimens. The problem arises fromthe fact that prior to the present invention, it was impossible toproduce a water suspension of levigated alumine. of the necessaryfineness, which was not,

subject to the objection that the aliunina would settle to the bottom ofthe water upon storing of the suspension, so as 'to produce a hardcakewhich could not easily be returned to suspension in spite of vigorousagitation. Because of this difllculty, metallographers have in the pastpurchased this material in bottled form from Germany where, by a secretart, it was produced tree from the objectionable caking described. Theneed for enabling the domestic production of this material isparticularly apparent at the present time. I

According to the present invention, as it is specifically practiced,hydrated alumina is placed loosely, without hard packing, to a depth ofabout two inches in an oxidation-resistant metal containerand heated fortwo hours at1850 F. The powder, when cooled, is transferred to. a glassvessel and shaken with water to which a few drops oi phenolphthalein hasbeen added in the'p roportion of from 109-150 g. elf-powder per 1000 cc.

I or water. At this stage the suspension is strongly alkaline, and eachparticle of alumina floats in the water ass. single unit; that is tosay, there is no tendency for the particles to agglomerate.

is well known, hydrated alumina contains an alkali, resulting from itsmanufacture, which cannot be driven oil by heating, this accounting foraaai'gnor to Delaware, a

mately 25% by;weignt oi thendians initially mixed in the water. thissediment being discarded.

At this stage the separated milky liquid represents a suspension oflevigated alumina which may be used for metallurgical polishing.biitwhen it is stored for any length oi time without being disturbed,the alumina suspension settles in form a hard cake which it is diihcultor impossible to break up again by agitation, such as by visomusiyshaking a bottle of the material.

Y periods without 'agitation. In'every respect it is the equal of thematerial formerly obtainable onlyfrom Germany. I I

To reduce the bulk-oi thema'torial, the clear liquid, whichultimately'sep'arat'es on standing, may be .syphoned oil until thesuspension reaches a concentration approximately 200 g. or alumina per1000 cc. cf water. This the alkalinity of the suspension. It is thistype oi' hydrated alumina with which this invention is concerned.Because the particles are unagglomerated, the coarser ones settle to thebottom quickly, whfle the liner ones remain in suspension i'or' a longertime, depending ontheir fineness. The previously described heating needI is diluted with from ao-so pal-tact water as his neededior use in thepolishing-ot metallographic specimens. I l

The material produced by this invention has been found satisfactory forpolishing all grades of steel, and does not produce scratches'visibleeven at high magnifications. A ilner suspension may-be required forsofter metals, such as'pure aluminum or lead. it'being understood thatthe longerthe initial water mixture 0! the alumina stands, the greaterwillbe the separation of the coarser particles from the liner-particles.Hownot be carried out" at the exact time and temperav tistosay. thehydrated alumina must be converted to alumina. I'he milky turedescribed, but it should be sumcient to condition the alumina so that itacts in the water ever the15 minute described hqein, is verysatisfactory for use with-steal specimens.

claim:

1. A method oi preparing alumina tor storing inwatersuspemion,comprising heating liquid, containing all the particles which have not Isettled-in 15 minutes, is syphoned out in a clean vessel, withoutagitation of the mixture such asmight disturb the settled, coarserparticles. The

coarse sediment'remaining represents approxihydrated alumina to convertit to alumina, said hydrated alumina an alkali resulting from themanufacture which cannot be driven with water and allowing tbemixture tostand, re:- a time permitting alumina I particles astosettletothcdoaircdilogmwhiletheflm ncnlloles lemolu ln ousoenslon onuooee ocel'lou oi on; wlllooul ogllullog one one eo'movlne; its uooeeoox'fclon one sueoeoelon water and allovnns the mix-lure to stand,

lo? a tlme permitting the coarser olnmlna poem else to settle to thedesired degree while the finer gialolcleo remain in suspension in theupper: gcorlrlon ol the inlxlme, w'ltlioue eqllellng the mixreinovlngits upper portion with one suspenslon oi the lone? particles, andsubstantially neullollzlng one removezl upper portion with aclrl toogglomeraoe its susnenslon oi time finer alumina particles to plevenetheir coking upon storing,

luitlel mixture lcemg colored with penolplilzllnleln and the acid usezllo'neu'bl' e the removed upper poillon lcelng nyclrocl'lloz'lc acidaclclell so no to just remove lat-s color.

A method of preparlng levlgatetl alumina ion storing in were? suspensloncomprising healing hyclzocecl olum'lna containing an alkali recull'lngfrom the manufacture 'wl'xlch cannot be clliven ofl, to a temperature ofaround 13:39 l

lo? a mine of about 2 hours to convei'l ll to alu= mine, mimng Juleollunlno when cool Wale? oevnoov colored with phenolphthaleln andallowing the nulltune to stand for a time permitting the courses:alumina oarticles to settle to the desired degree while the linerparticles remain in suspension in the upper portion of the mixture,Without agitatlng the mixture removing its upper portion with thesuspension offlner particles, and adding hydrochloric acid to theremoved upper portion so as to just remove its color and substantiallyneutralize it to agglomerate its suspension of the finer aluminaparticles to prevent; their coking upon storing. j

4. A method of preparing levlgatecl alumina for storing in watersuspension, com-pulsing heating hydrated alumina containing an alkaliresultlnz from the manufacture which cannot Zoe driven off, Whileloosely placed in a container to a temperature of around 1850 F. for atime of about 2 hours to convert it to alumina, ohls alumina when coolwith water colored with phenolphthelein and allowing the mixture tostand for about 15 minutes so that about 25% by Weight of the aluminaoriginally mixed with the Water settles as coarser particles while theremaincler remains as finer particles in suspension in the upper portionof the mixture, Without 23llutlzog the mixture removing its upperportion with the suspension of finer particles, and adding hydrochloricacid to the removed upper "portion so as to just, remove its color and.substantlolly neutralize it to agglomerate its suspension of line fineralumina particles to prevent their cokin upon storing.

JOSEPH

